A wind turbine 1 as shown in FIG. 1 consists of several large single parts that are each preassembled at a factory workshop. A tower 2 of the wind turbine 1 can reach a height of 100 meters or 150 meters or even more and typically consists of tube segments 3 with a length of for instance 20 meters or 30 meters with circular flange connections on each side of the tube segments 3. During erection of the wind turbine 1 on site, the tube segments 3 are fitted together and connected with the joint circular flange connections with bolts and nut bolts. Large quantities of bolts, typically in the hundreds, of large size are necessary to establish the required stiffness and strength of the connections. In order to achieve the appropriate defined stiffness and strength in the joints all the bolts have to be bolted down with a predefined preload or torque.
During the erection of the wind turbine the bolt nuts are today typically applied and pretightened manually. This is followed by a manual procedure that applies the specified preload to the nut bolts. During this procedure a hydraulic high torque wrench is typically used. Several factors or parameters influence the quality of the tightening process, including the temperature of the working environment, the temperature of the hydraulic fluid, and the available oil pressure that is supplied to the hydraulic torque wrench.
The tightening of every bolt is typically done manually and a high level of quality is needed in order to ensure the stiffness and strength of the wind turbine. The tightening process is a very risky job that can take up to several days for one wind turbine 1. In case that the tower 2 of the wind turbine 1 collapses, possibly years after it was erected, it is difficult to analyze the causes of such an accident and to document whether the bolts were tightened according to the specifications prior to the collapse.
The invention is further seeking to alleviate the physical deterioration and work related illnesses that the monotonous and repetitive job with vibrating equipment is resulting in.